1. Field of the Invention
The present invention relates to high temperature superconductor compositions, electrical conductors produced using such compositions and to methods of producing such compositions and conductors.
2. Related Art
High temperature superconducting oxides include yttrium-barium-copper oxides and related materials. For example, the composition YBa2Cu3O7−δ (referred to herein and in the academic literature as YBCO) is a superconductor at temperatures below a critical temperature Tc, which varies with the value of δ.
Improvement of flux pinning and thus the amount of current that can be carried in YBCO (in self-field and/or in applied field) is important for achieving widespread applications of this technologically important material. Practical pinning enhancement methods developed within the last 5 years such as incorporating nanoinclusions in the film or on the substrate surface, disorder effects from rare earth (RE) modifications, and microstructural modification have all been successful to some extent in specific field and temperature regimes. These pinning enhancement methods are described further in References 1-12.
Reference 1 describes the formation of BaZrO3 (BZO) particles in YBCO films grown on strontium titanate (either as a single crystal substrate, as a buffer layer on MgO single crystal, or as a buffer layer on MgO formed on nickel-based alloy). 5 mol % BaZrO3 was used. Compared with similar YBCO films formed without BaZrO3, the YBCO films incorporating BaZrO3 provided significantly improved Jc in magnetic field strengths (μ0H) up to 7 T at 75.5 K. US 2006/0025310 discloses similar subject matter to Reference 1.
Reference 12 discloses films of YBCO-BZO formed on (001) STO single crystal substrates. This document confirms, based on the angular dependence of Jc with the direction of applied field, the c-axis alignment of columnar pinning centres in the YBCO-BZO film. However, Tc is reduced with increasing BZO content.
Reference 13 discloses the formation of YBCO-BZO films on CeO2-buffered textured nickel alloy substrates. The BZO particles are considered to have a c-axis aligned “bamboo” structure.
Reference 21 discloses the incorporation of BaNb2O6 (BNO) into ErBa2Cu3Oy films grown on (001) STO substrates. ErBa2Cu3Oy is structurally related to YBCO. BNO was incorporated into ErBa2Cu3Oy at concentrations of 0.5 and 1.5 wt %. Self-field Jc decreased with increasing BNO concentration at 77K, although Jc at >0.5 T increased with increasing BNO concentration at 77K. TEM investigations indicated that BNO particles formed as c-axis aligned nanorods. Reference 22 suggests that the composition of the nanorods is Ba(Er0.5Nb0.5)O3.